The present invention relates to an apparatus for detecting displacement of a mechanical element, particularly to an apparatus for detecting displacement of a mechanical element driven by an actuator in accordance with a magnetic flux generated by a magnet magnetized in displacement direction.
Various methods for detecting the displacement have been proposed. Japanese Patent No. 2749748 discloses the method for detecting displacement of a movable magnet member by measuring a magnetic-flux density in a gap between an electromagnet and the movable magnet member. Moreover, as another embodiment in the specification, a method for detecting the displacement of the movable magnet member by measuring a capacitance in a gap between an electromagnet and the movable magnet member is disclosed. Furthermore, methods for detecting the displacement has been proposed, for example, by detecting an eddy current or by the use of a differential transformer.
In the case of an actuator for generally driving a mechanical element, a mechanical element is not only driven through mechanical driving by connection of a cam with a rod but also it is electro-magnetically driven. An electromagnetic actuator drives a mechanical element by attracting an electromagnet by exciting an electromagnetic coil in accordance with an electrical signal. In the case of driving the electromagnetic actuator, because the driving timing and driving force can be optionally changed by controlling electrical signals, it is frequently used in a field requiring precise timing control or variable control.
Also in the case of a vehicle, an actuator is used for various portions including an idle control valve, fuel injection valve, and EGR control valve of an engine. Particularly, it is desired to apply an electromagnetic actuator to intake/exhaust valves of an engine as a future possibility. A system for mechanically changing the timing of intake/exhaust valves of an engine in accordance with engine rotation has been practically used. By driving intake/exhaust valves by an electromagnetic actuator, it is possible to flexibly control the valve timing and improve the output characteristics and fuel consumption of an engine.
Intake/exhaust valves of the engine of a vehicle need to be opened and closed at a high speed, which requires an accurate timing in either of mechanical driving and electromagnetic driving. Therefore, it is necessary to accurately detect displacement of a mechanical element for driving an actuator so that the valve timing can be properly controlled.
Displacement detection by the above-described methods has problems of high cost because shielding lines are used to obtain a preferable S/N ratio. The number of harnesses and the number of parts are increased because driving signals are different from detection signals and a wave-shaping circuit is required. Displacement detection is subject to disturbance because of detecting a feeble signal, and it is difficult to obtain stable outputs. Moreover, to obtain a linear output characteristic at the time of measuring a magnetic-flux density of a gap, it is necessary to measure magnetic-flux densities of upper and lower gaps, which gives rise to a problem of increasing number of parts.
Therefore, it is an object of the present invention to provide a displacement detecting device having an inexpensive structure and capable of detecting displacement of a mechanical element without increasing the number of harnesses and the number of parts.
It is another object of the present invention to provide a displacement-detecting device capable of providing linear output of displacement of a mechanical element.
It is further object of the present invention to provide a displacement-detecting device capable of reducing the effect of disturbance.
In accordance with one aspect of the invention, the displacement detecting device comprises a mechanical element capable of being displaced, a magnet connected to the mechanical element and magnetized in displacement direction of the mechanical element, and a magnetic sensor for detecting a magnetic flux generated by the magnet and outputting a sensor output corresponding to the detected magnetic-flux value, and detects displacement of the mechanical element in accordance with the sensor output. The displacement-detecting device has a simple structure with limited number of parts.
In accordance with another aspect of the invention, the displacement-detecting device has a configuration in which the magnetic sensor is a Hall element and the sensor output is a Hall voltage. Because a Hall element produces a Hall voltage proportional to a magnetic-flux density, it is possible to obtain a linear output for displacement. Reliable output is obtained with a simple structure.
In accordance with further aspect of the invention, the displacement-detecting device has a configuration in which the length of displacement direction of the magnet is larger than the distance of movement of the mechanical element and the quantity of magnetic flux detected by the magnetic sensor changes linearly with respect to displacement of the magnet. A linear output is obtained with respect to displacement.
In accordance with yet another aspect of the invention, the displacement-detecting device has a configuration in which the magnet is connected to the mechanical element through a non-magnetic member or a material having characteristics close to the non-magnetic material. Because the magnet is connected to the mechanical element through a non-magnetic member or a material having characteristics close to the non-magnetic material, the magnetic sensor is able to detect a magnetic flux generated by the magnet without significant disturbance in a magnetic field.
In accordance with one embodiment, the mechanical element is an intake/exhaust valve of an engine. Accuracy of the valve timing controlled by an actuator is improved.
In accordance with one aspect of the invention, the magnet is provided on a spring seat supporting a spring, and the spring seat is connected to the intake/exhaust valve via a transfer shaft. The magnetic sensor is provided between the magnet and the spring. The magnetic sensor detects magnetic flux in the horizontal direction generated by the magnet and outputs a voltage proportional to displacement of the magnet. Thus, the detection of displacement of the intake/exhaust valve is facilitated.
In accordance with another aspect of the invention, a magnetic material or magnet is provided between the magnetic sensor and the spring. The effect of the spring on the magnetic flux generated by the magnet is reduced, accuracy of the detection of displacement of the intake/exhaust valve being improved.
In accordance with yet another aspect of the invention, the magnet is connected to the intake/exhaust valve via a transfer shaft that is made of a non-magnetic member or a material having characteristics close to the non-magnetic material. The effect of leakage flux is reduced, accuracy of displacement of the intake/exhaust valve of the engine being improved.
In accordance with yet another aspect of the invention, the magnet is provided on a spring seat connected to the transfer shaft, and the spring seat is made of a non-magnetic member or a material having characteristics close to the non-magnetic material. Because the spring seat is made of a non-magnetic member or a material having characteristics close to the non-magnetic material, the magnetic sensor is able to detect a magnetic flux generated by the magnet without significant disturbance to the magnetic field.
In accordance with yet another embodiment, the magnet is a cylindrical permanent magnet. Because a magnet can be easily fixed so as to connect with the transfer shaft of an actuator, the detection of displacement of the mechanical element by detecting magnetic flux from the magnet is implemented with a simple structure.